MEMS piezoresistive acceleration sensor

Abstract

An acceleration sensor includes a fixing portion, a weight portion, a detection beam, support beams, and a metal wiring. The weight portion is supported on the fixing portion so as to be freely displaced. The detection beam is connected to the fixing portion and the weight portion and piezoresistive elements are provided on the detection beam. The support beams are provided separately from the detection beam and are connected to the fixing portion and the weight portion. Both ends of the metal wiring are extended to the fixing portion and the metal wiring is wired so as to pass through the support beams.

What is claimed is: 
     
       1. An acceleration sensor comprising:
 a fixing portion; 
 a weight portion that is supported on the fixing portion so as to be freely displaced; 
 a detection beam that is connected to the fixing portion and the weight portion and on which a piezoresistive element is provided; 
 a support beam that is provided separately from the detection beam and is connected to the fixing portion and the weight portion; and 
 a wiring portion, both ends of which are extended to the fixing portion, and that is wired so as to pass through the support beam; wherein 
 the detection beam and the support beam are located between the weight portion and the fixing portion. 
 
     
     
       2. The acceleration sensor according to  claim 1 , wherein among the fixing portion, the weight portion, the detection beam, and the support beam, at least the supporting beam includes a silicon substrate and the wiring portion includes an injection wiring including impurities in the silicon substrate. 
     
     
       3. The acceleration sensor according to  claim 1 , wherein the wiring portion includes an enlarged wiring width portion on the support beam. 
     
     
       4. The acceleration sensor according to  claim 1 , wherein the piezoresistive element is connected to the wiring portion. 
     
     
       5. The acceleration sensor according to  claim 1 , wherein the acceleration sensor is a micro-electro-mechanical systems piezoresistive acceleration sensor. 
     
     
       6. The acceleration sensor according to  claim 1 , wherein the piezoresistive element is included in a Wheatstone bridge. 
     
     
       7. The acceleration sensor according to  claim 1 , wherein the fixing portion includes a projecting portion that projects toward a side of the weight portion and at least two recess portions. 
     
     
       8. The acceleration sensor according to  claim 1 , wherein the weight portion includes a recess portion that is recessed toward a side opposite a side of the fixing portion and at least two projecting portions. 
     
     
       9. The acceleration sensor according to  claim 1 , wherein the support beam is a first support beam, a second support beam is provided such that the detection beam is located between the first and second support beams. 
     
     
       10. The acceleration sensor according to  claim 1 , wherein the weight portion and the fixing portion are rectangular or substantially rectangular, and the detection beam and the support beam are flat plate-shaped. 
     
     
       11. The acceleration sensor according to  claim 1 , wherein the piezoresistive element is a first piezoresistive element, and a plurality of additional piezoresistive elements are provided to define a Wheatstone bridge with the first piezoresistive element. 
     
     
       12. The acceleration sensor according to  claim 11 , further comprising a plurality of wirings connected to respective ones of the piezoeresistive elements. 
     
     
       13. The acceleration sensor according to  claim 1 , wherein a metal wiring and injection wirings are electrically connected to each other, and are wired on a path starting from the fixing portion, passing through the support beam, the weight portion, and another support beam in this order, and returning to the fixing portion again. 
     
     
       14. The acceleration sensor according to  claim 1 , wherein the metal wiring is not provided on regions overlapping the support beam and the another support beam, and the injection wirings are located on the regions overlapping the support beam and the another support beam. 
     
     
       15. The acceleration sensor according to  claim 14 , wherein the injection wirings include enlarged width portions that are larger than a width of the metal wiring, and the enlarged width portions overlap the support beam and the another support beam. 
     
     
       16. The acceleration sensor according to  claim 15 , wherein the width of the metal wiring is equal or substantially equal to the widths of the injection wirings only at connection ends where the metal wiring is connected to the injection wirings. 
     
     
       17. The acceleration sensor according to  claim 1 , wherein a plurality of metal wirings are provided on the fixing portion and a plurality of metal wirings on the weight portion. 
     
     
       18. An acceleration sensor comprising:
 a fixing portion; 
 a weight portion that is supported on the fixing portion so as to be freely displaced; 
 a detection beam that is connected to the fixing portion and the weight portion and on which a piezoresistive element is provided; 
 a support beam that is provided separately from the detection beam and is connected to the fixing portion and the weight portion; and 
 a wiring portion, both ends of which are extended to the fixing portion, and that is wired so as to pass through the support beam and the weight portion; wherein 
 the detection beam and the support beam are located between the weight portion and the fixing portion. 
 
     
     
       19. An acceleration sensor comprising:
 a fixing portion; 
 a weight portion that is supported on the fixing portion so as to be freely displaced; 
 a detection beam that is connected to the fixing portion and the weight portion and on which a piezoresistive element is provided; 
 a support beam that is provided separately from the detection beam and is connected to the fixing portion and the weight portion; and 
 a wiring portion, both ends of which are extended to the fixing portion, and that is wired so as to pass through the support beam and connected to circuit terminals for characteristic screening; wherein 
 the detection beam and the support beam are located between the weight portion and the fixing portion.